The present invention is directed to hydraulic suspension systems and, more particularly, to linear actuators for hydraulic suspension systems.
Automobiles, including trucks and sport utility vehicles, as well as other motor vehicles, incorporate suspension systems designed to minimize the leaning or “rolling” of the vehicle body relative to the frame or wheels that occurs when the vehicle corners or turns at relatively high speeds.
FIG. 1. illustrates a typical suspension system, generally designated 10, that includes a pump 14 driven by a motor 12 that draws hydraulic fluid from reservoir 16 through supply line 18. The output of pump 14 is conveyed through line 20 to manifold 22. Fluid flow is split at 24 and is further conveyed through line 26 to power steering manifold 28 and along lines 30, 70 to solenoid valves 32, 34.
Lines 36, 38 extend from solenoid valve 32 and are in fluid communication with rod chamber 40 and piston chamber 42, respectively, of front actuator 44. Lines 46, 48 extend from solenoid valve 34 and are in fluid communication with rod chamber 50 and piston chamber 52, respectively, of rear actuator 54. Fluid supply lines 64, 66 are connected to enable valve 32 to supply fluid to lines 46, 48, respectively, and thereby pressurize rear actuator 54 at the same time as the front actuator 44.
Line 56 is connected to a pressure control valve 58 and a relief valve 60 that, in turn, are connected to line 62, which returns fluid to the reservoir 16. Lines 68, 70 connect valves 32, 34 to return line 62 and supply line 30, respectively.
A controller (not shown) actuates valve 32 to displace its spool from the position shown in FIG. 1, thereby opening lines 36, 38 to receive pressurized fluid from line 30, pressurizing rod chamber 40 and piston chamber 42 of front actuator 44 and, through supply lines 64, 66 and 46, 48, pressurizing rod chamber 50 and piston chamber 52 of rear actuator 54. This orientation causes the front and rear actuators 44, 54, respectively, to extend.
When valve 32 is actuated such that the spool is in the position shown in FIG. 1 (i.e., the unopened position), and valve 34 is actuated such that the spool is displaced from the configuration shown in FIG. 1 (i.e., the open position), pressurized fluid flows through supply lines 30, 70, to valve 34, and from valve 34 through line 64 and line 36 to the rod chamber 40 of front actuator 44 and through line 46 to the rod chamber 50 of rear actuator 54. At the same time, fluid in piston chambers 42, 52 of front and rear actuators 44, 54 flows through lines 38, 48, 66 to valve 34, and from valve 34 through return lines 68, 62 to the reservoir 16. Accordingly, the front and rear actuators 44, 54 are retracted.
Thus, by selectively pressurizing the front and rear actuators 44, 54 (which, for example, would both be mounted on one side of a vehicle) by appropriately opening and closing solenoid valves 32, 34, the associated vehicle may be leveled.
When the actuators 44, 54 receive a shock load, such as by actuator 72 (which schematically shows a test stand associated with the suspension system 10 that is designed to simulate a vehicle associated with the suspension system encountering a bump or bumps), the shock causes the pistons 74, 76 to be displaced relative to the cylinders 78, 80. The displacement is facilitated by check valves 82, 83 within the pistons 74, 76 of actuators 44, 54, respectively.
A disadvantage with such systems is that the shock imparted to the actuators 44, 54 is, in turn, transmitted to the associated supporting structure, such as a vehicle body, through bushings 84, 85 (or other actuator mountings), resulting in discomfort to passengers and possible damage to associated components.
In an effort to reduce the transmission of shock, such actuators have been modified as shown in FIG. 2. The actuator 86 shown in FIG. 2 includes a piston 87, a cylinder 88, a piston chamber 89, a rod chamber 90, an annular disk 91 and a piston rod 92. The piston 87 includes a plurality of orifices 93 therethrough that interconnect the piston chamber 89 with the rod chamber 90. The rigid, annular disk 91 extends about the piston rod 92 and is spring-biased (via spring 94) to cover the orifices 93 when the pressure in the piston chamber 89 and rod chamber 90 are equal and in conditions when the piston 87 and piston rod 92 are being forced out from the associated cylinder 88 of actuator 86. However, when a force, indicated by arrow F, is applied to piston rod 92, as by a shock load imparted to the actuator 86, thereby forcing piston 87 into cylinder 88, the flow of fluid from the piston chamber 89 to the rod chamber 90 through orifices 93 displaces the disk 91 away from the piston 87 (i.e., against the bias of spring 94), thereby facilitating the flow of fluid from the piston chamber 89 to the rod chamber 90. The presence of the disk 90 retards the flow of fluid and lessens the shock transmitted to the associated vehicle.
Nevertheless, a disadvantage with such actuators and systems is that there is noise associated with the rapid displacement of the piston 87 resulting from the flow of fluid around the annular disk 91 in response to a shock load and the aeration and compression of hydraulic fluid within the actuators. Accordingly, there is a need for an actuator for use in a suspension system in which the noise associated with rapid displacement of the actuator is minimized.